1. Field of the Invention
The present invention relates to the manufacture of a joint between metal and a ceramic substrate, more particularly to a method of manufacturing a high reliability joint between metal and a ceramic substrate for a high temperature sensor.
2. Description of the Related Art
High temperature sensors comprising a ceramic material, a joint, and a metal wire have been widely used at high temperature (exceeding than 800xc2x0 C.) and thermal cycle environments such as the engine of an automobile.
Ceramic materials such as aluminum oxide, silicon carbide, or silicon nitride are typically bonded with ionic bonds or covalent bonds and have brittle properties. Metallic materials have metallic bonds and are tough. In addition, thermal expansion coefficients of the metallic materials are generally larger than those of the ceramic materials. The different thermal expansion coefficients between the ceramic materials and the metallic materials result in thermal stresses at the joint or interface between these materials after joining. Moreover, the tensile thermal stresses are generated within the ceramic materials so that the joint or the ceramic materials will be damaged.
Therefore, it is important to develop methods to decrease the thermal stresses near the interfaces between ceramic materials and metallic materials. One method to reduce or eliminate the thermal stresses is to use an inter-layer, serving as the joint, with a multiple-layer structure between the ceramic materials and the metallic materials. The inter-layer must have high toughness, adapted thermal expansion coefficient, and low yield strength, providing plastic deformation during thermal cycle so as to decrease the thermal stresses.
Nonetheless, it is difficult to find a suitable stacked composition for the inter-layer material. Furthermore, the inter-layer can accumulate large plastic deformations during repeated thermal cycles. As a result, the inter-layer is susceptible to damage under many heating and cooling cycles.
Another method to reduce or eliminate thermal stresses is to use functionally graded materials (FGMs) to serve as the joint materials. That is to say, the thermal expansion coefficient of the joint element gradually alters by mixing and sintering of a specific ratio of different materials. However, the composition of functionally graded materials is not easily adjusted.
Even with the advancements mentioned above, there remains a considerable and continuous effort to further improve the high temperature durability of a joint between a metallic material and a ceramic substrate by selecting a material having an adopted thermal expansion coefficient for the joint component.
In view of the above disadvantages, an object of the invention is to provide a method of manufacturing a joint between metal and a ceramic substrate for a high temperature sensor. The joint has good high temperature durability, enhanced thermal fatigue resistance and high reliability so that the sensor is suitable for an environment having elevated temperature, vibration, or thermal cycles.
Accordingly, the objects are attained by providing a method of manufacturing a joint between metal and a ceramic substrate for a high temperature sensor. First, a predetermined hole is formed in the ceramic substrate to serve as a joint portion. A bonding layer is preferably disposed on the ceramic substrate to form on the inner surface and the surrounding portion of the hole. Next, the hole is filled with a supporting metal. Then, a conductive layer is formed on the supporting metal and the bonding layer. A metal signal conductive frame is then formed on the conductive layer. Next, a welding spot is formed through the metal signal conductive frame, the conductive layer and the supporting metal at the joint portion by a welding process.
A further object of the invention is to provide a method of manufacturing a joint between metal and a ceramic substrate for a high temperature sensor. The formation of the bonding layer can further comprise the steps of:
mixing a precious metal powder and a ceramic powder to form a mixture;
coating the mixture on the ceramic substrate; and
sintering the mixture to generate a bonding layer.
Moreover, the formation of the conductive layer further comprises the steps of:
mixing 50-99% by weight of a precious metal powder and 1-50% by weight of a ceramic powder to form a mixture;
coating the mixture on the ceramic substrate; and
sintering the mixture to generate a conductive layer.
In accordance with one aspect of the invention, there is provided a method of manufacturing a joint between metal and a ceramic substrate for a high temperature sensor. The supporting metal is preferably a nickel-based alloy, a cobalt-based alloy, an iron-based alloy, a metal matrix composite, or platinum.
In accordance with another aspect of the invention, there is provided a method of manufacturing a joint between metal and a ceramic substrate for a high temperature sensor. The formation of the supporting metal further comprises of the steps of:
providing a metallic material of a solid rod, a sheet material, or a powder; and
pressing and/or sintering the metallic material to form a supporting metal.
In accordance with further aspects of the invention, there is provided a method of manufacturing a joint between metal and a ceramic substrate for a high temperature sensor. The metal signal conductive frame is preferably a nickel-based alloy, a cobalt-based alloy, or an iron-based alloy.
In accordance with a still further aspect of the invention, there is provided a method of manufacturing a joint between metal and a ceramic substrate for a high temperature sensor. The welding process is preferably laser-beam welding, electron-beam welding, tungsten inert gas welding, plasma-arc welding, or resistance welding.